The invention relates to a method for operating an internal combustion engine, especially of a motor vehicle, wherein a catalytic converter is charged with hydrocarbons and wherein the conversion capability of the catalytic converter is determined. Likewise, the invention relates to a control apparatus for an internal combustion engine, especially of a motor vehicle, as well as an internal combustion engine especially for a motor vehicle.
A method of this kind, a control apparatus of this kind and an internal combustion engine of this kind are, for example, known for a so-called intake manifold injection. There, the fuel is injected into the intake manifold of the engine during the induction phase. The hydrocarbons developed during the combustion of the fuel are converted, inter alia, into carbon dioxide in the catalytic converter. It is known that the catalytic converter is subjected to deterioration which leads to a limiting of its converting capability.
The method mentioned initially herein is also known from a direct-injecting internal combustion engine. There, the fuel is injected directly into the combustion chamber of the engine, inter alia, during the induction phase. The arising exhaust gases are purified by a downstream catalytic converter.
It is an object of the invention to provide a method for operating an internal combustion engine with which the deterioration of the catalytic converter is detected.
This object is achieved in accordance with the invention in a method of the above-mentioned type in that the converting capability of the catalytic converter is determined by means of a combination of a passive and of an active diagnostic method. The task is correspondingly solved in a control apparatus and an internal combustion engine of the respective types referred to above. The present invention can be utilized in the same manner for an intake manifold injection as for a direct-injecting internal combustion engine.
With the passive diagnostic method, it is possible to recognize the conversion capability and therefore the state of deterioration of the catalytic converter rapidly and without an effect on the control (open loop and/or closed loop) of the engine. However, if the catalytic converter is in a transition region between good converting capability and poor converting capability, the passive diagnostic method is supplemented or replaced by an additional active diagnostic method. This active method can recognize the conversion capability very accurately and can thereby recognize the deterioration of the catalytic converter.
In total, with the invention, a method is provided with which the deterioration of the catalytic converter can be determined rapidly but nevertheless very precisely and a necessary exchange of the catalytic converter can be reliably detected.
In an advantageous further embodiment of the invention, respective indices for the conversion capability of the catalytic converter are generated with the passive and the active diagnostic methods, respectively, which are applied by an evaluation for determining the conversion capability. This index for the conversion capability can be based especially on a comparison of a measurement quantity and a reference quantity. The measurement quantity can, for example, be a temperature of the exhaust gas downstream of the catalytic converter.
It is especially advantageous when an activation signal is generated by the passive diagnostic method when the conversion capability of the catalytic converter lies in the transition region from good to poor. Here, the active diagnostic method is preferably activated by the activation signal. In this way, it is possible in a simple manner to bring the active diagnostic method into use precisely when the passive diagnostic method does no longer ensure an adequate accuracy. The interventions, which are required in the active diagnostic method, are then limited to a minimum in the control (open loop and/or closed loop) of the engine.
In an advantageous further embodiment of the invention, the index for the conversion capability of the catalytic converter, which is generated by the active diagnostic method, is preferred over the index, which is generated by the passive diagnostic method. Alternatively, it is likewise possible that a supplementation takes place, for example, in the sense of a weighting or the like.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus, especially on a microprocessor, and is suitable for executing the method in accordance with the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for whose execution the program is suitable. As a control element, an electric storage medium is especially applicable, for example, a read-only-memory or a flash memory.